Friday, Feb 04, 2011 at 18:11
@Derek,
If a battery expands like that while it's not being charged, there need to be a number of concurrent faults:
1) An internal short which creates enough heat to boil off some of the water inside the battery.
2) The overpressure valves open on a regular basis every time the battery gets re-charged. This doesn't seem to be the case with this battery because the internal pressure obviously was enough to bulge the walls at this relatively low wall temperature of 49 degrees. There is already a discrepancy: steam pressure only develops near 100 degrees, but the case temperature was only measured being 49 degrees, a temperature gradient of 50 degrees inside a few mm thick plastic wall?
3) Note that the battery is visibly swollen on 3, possibly 4 sides. That means that not only one cell failed but likely all six of them.
Considering that each cell has its own overpressure valve, all six valves must have failed concurrently.
So there was a failure in a number of cells, plus in a number of overpressure valves?
I don't want to have a crack at the odds for something like this to happen in a single occurrence.
And then, the author admits to have had 3 swollen batteries by different manufacturers within the space of one month...
Hmm, if it was me I'd toss out my battery charging gear - or maybe he uses his beloved DC arcwelder for charging and glued the overpressure valves shut to stop them from making annoying noises?
@oldtrack123,
the whole van airspace is not irrelevant because the highly volatile hydrogen gas will quickly disperse after escaping from the battery, within this volume AND beyond, i.e. to the outside.
And I don't have to mention that a pilot flame needs to be placed in a vented space otherwise it would simply run out of oxygen.
This vented space is more than enough to also vent any traces of hydrogen escaping from the battery, yes that's ANY battery for that matter (VRLA batteries are a bit safer in this regards, because the pathway for external flames to the inside is restricted by the valves - just in case someone wanted to try this by pointing a flame at the vents/valves).
Back to the vented space of
the pilot, at this extremely low concentration of H2 gas outside the battery, no flame in the world will ignite it, so the traces of H2 will safely vent together with the hot combustion products of
the pilot flame.
You'd have to forcefully open the battery and ignite the gas inside at the same split second of opening it - before all the combustible hydrogen's gone - if you wanted to make it go bang.
How many folks keep their batteries inside a caravan, where there are all sorts of naked flames i.e. pilot flames, gas cookers, lighters...
Can you give me one single example where it has been proven that the tiny traces of hydrogen escaping from a battery have built up sufficiently inside a van to cause an explosion?
And please kindly note that in the linked example of a swollen battery, the culprit is steam pressure and not hydrogen...
cheers, Peter
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